The proposed work is designed to investigate specific aspects of B cell differentiation in normal and abnormal conditions and to elucidate mechanisms of specific models of B cell activation. Cell separation techniques, chromosome markers, and in vivo and in vitro methods are employed in these experiments. Specifically, experiments are designed to further define the apparent existence of separate lineages for precursor B and precursor T cells in embryonic bone marrow of chick embryos. Selective in vitro methods are employed to obtain separate populations of the precursor cell pools. Their functional capacity is then tested following transfer to appropriate recipients. Additional work is concerned with defining conditions allowing prolonged in vitro survival of precursor B cells utilizing feeder layers and factors of various tissue origins in order to define differentiation steps of precursor cells to functional B cells.